1. Field of the Present Invention
The present invention relates to an organic electroluminescence device.
2. Description of the Related Art
Research and development concerning various display devices are being actively carried out, and, among these, an organic electroluminescence device (hereinafter also referred as an “organic EL device”) is attracting attention as a promising display device as it can provide a light emission of a high luminance at a low voltage.
In recent development of the organic EL devices, various research is being carried out for reduction in driving voltage, improvement in durability, and improvement in external quantum yield.
As a technology for enabling light emission at a low voltage, utilization of a copper phthalocyanine or an amine compound as a hole injection material has been reported. However, devices utilizing known hole injection materials are associated with disadvantages of a decrease in luminance and generation of a dark spot (non-light-emitting portion) in the case of prolonged light emission or prolonged storage at a high temperature.
A device containing a phosphorescence emitting metal complex such as a trisphenylpyridine iridium complex disclosed in WO 00/070655 or an octaethylporphyrin platinum complex disclosed in U.S. Pat. No. 6,303,238B1 or 6,653,564B1 shows a high external quantum efficiency and is attracting attention.
However, devices containing such a phosphorescence emitting material are unsatisfactory in durability, and further improvement is desired.
On the other hand, mass production methods for a panel include a vacuum deposition method utilizing a low molecular material, an ink jet method utilizing a high molecular material, and a printing method, but a wet coating method is being investigated as a method capable of easily realizing a large area device.
However, because many of the metal complexes such as described above, have a strong intermolecular interaction and form a molecular associate, they have an extremely low solubility in a solvent, and a uniformly dissolved wet coating liquid is difficult to prepare. Also, because of the low solubility, they are difficult to contain at a high concentration in a film, and are therefore disadvantageous with respect to durability of the device.
Moreover, because such metal complexes form a molecular associate even in the organic EL device and exhibit a light emission of a different wavelength derived from such associate, the color of light emission becomes impure and a light emission of a high saturation is difficult to obtain.
On the other hand, JP-A No. 2003-77675 discloses a device prepared by wet coating utilizing a polymer bonded with a metal complex such as an iridium complex, but such a device has some disadvantages such as low light emission efficiency, poor driving durability and the like, and further improvement is therefore desired.